1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying apparatus or a printer, for forming an image on a recording material utilizing an electrophotographic process.
2. Related Background Art
Current electrophotographic image forming apparatuses widely employ a dismountably mounted process cartridge integrating a photosensitive drum, a developing device and the like thereby facilitating maintenance or toner replenishment. Such a process cartridge is required to contain a toner of an amount corresponding to a service life of the photosensitive drum defined by a deterioration thereof, and therefore tends to become bulky.
Since the consumed toner amount varies significantly depending on the density of images formed by the user, the cartridge has to be replaced when the deterioration of the photosensitive drum or the consumption of the toner reaches a certain amount, and such cartridge replacement at a somewhat early stage when the photosensitive drum or the toner has a certain remaining capacity tends to increase the running cost.
For this reason, there has recently been commercialized an image forming apparatus in which a process cartridge and a toner cartridge for supplying a toner to a developing device in the process cartridge are constructed separately and rendered respectively mountable.
For example, as shown in FIGS. 12A and 12B, four process cartridges 200 for respectively forming yellow, magenta, cyan and black color images, and four toner cartridges 202 for respectively toner supply to the process cartridges 200 are mounted on a main body 201 of an apparatus, and toner images formed on photosensitive drums 200a in the process cartridges 200 are primary transferred in succession onto an intermediate transfer belt 203, and the primary transfer images are secondary transferred in a secondary transfer part 206 onto a transfer material conveyed from a sheet cassette 204 by conveying rollers 205. Then, such transfer material is conveyed to a fixing device 207 for heat fixation of the toner images and is discharged onto a discharge portion 208 in an upper part of the apparatus.
Such separation of the toner cartridge from the process cartridge enables a replacement of each cartridge according to the consumption in the running operation of each cartridge, thereby reducing the running cost.
Patent literature 1: Japanese Patent Application Laid-Open No. H06-110337;
Patent literature 2: Japanese Patent Application Laid-Open No. 2003-202792.
However, in a prior image forming apparatus in which the process cartridges 200 and the toner cartridges 201 are individually mounted, the process cartridges 200 are positioned inside a frame member 209 of a main body 202. On the other hand, the toner cartridges 201 are positioned in an overlapping manner with the process cartridges 200, in a Z-axis direction which is a direction of a rotary axis of photosensitive drums 200a incorporated in the process cartridges 200. Further, as the toner cartridges 201 are positioned above the process cartridges 200 for toner supply thereto, the process cartridges 200 and the toner cartridges 201 mutually overlap also in a Y-axis direction.
Therefore, in case of a replacement of the toner cartridge 201, as shown in a lateral view in FIG. 13, cartridge replacement covers 210, 211 are opened and a toner cartridge 201 is taken out.
In case of a replacement of the process cartridge 200, the configuration requires operations of at first temporarily detaching a toner cartridge 201, then removing a process cartridge 200, then setting a new process cartridge 200, and setting the temporarily detached toner cartridge 201 on the set process cartridge 200.
Therefore, the user operability is poor in the replacement of the process cartridge. Also in case of the replacement of the process cartridge, as the toner cartridge is temporarily detached in a state containing remaining toner, the toner may drop from the toner cartridge 201 and may be scattered in the apparatus since the toner cartridge 201 is positioned in the frame member of the main body.
Furthermore, as exposure means 212 are positioned above the photosensitive drums 200a, the image transferred from the photosensitive drum 200a to the intermediate transfer belt 203 travels from P1 to P2 as shown in FIGS. 12A and 12B, so that the primary transferred image has to be conveyed over a long moving distance Q1 before the secondary transfer. Therefore the user has to wait a corresponding time for obtaining a printout, and there results a long first print time.
On the other hand, there can be conceived an image forming apparatus as shown in FIGS. 14A and 14B, in which exposure means 212 is positioned below the process cartridges 200 and the intermediate transfer belt 203 is positioned above the process cartridges. In such configuration, a moving distance Q2 of the image, transferred from the photosensitive drum 200a to the intermediate transfer belt 203, to the secondary transfer is shortened, thereby reducing the first printout time.
However, also in this configuration, the process cartridges 200 and the toner cartridges 201 are superposed in the direction of the rotary axis of the photosensitive drums 200a and in the direction of height of the apparatus, so that the toner cartridge 201 has to be removed at first in case of replacing the process cartridge 200. Also, as the exposure means 212 is positioned below the process cartridges 200 and the toner cartridges 201, a toner 213 spilt at the removal of the toner cartridge 201 may be deposited on the exposure means 212.